Using travertine deformations to characterize paleoseismic activity along an active oblique-slip fault: the Alhama de Murcia fault (Betic Cordillera, Spain)

Abstract

A preliminary paleoseismic study of trave rtine deposits cut by an active oblique-slip fault is presented. The Alhama de Murcia fault affects late Pleistocene and Holocene travertine deposits along the Lorca-Totana segment. Travertines along oblique-slip (reverse-sinistral) active faults have not been reported. On the Alhama de Murcia fault, CaCO3 rich springs are linked to an extensional step-ove rand to releasing fault junctions in a reverse-sinistral fault zone. The sampling methodology for U/Th dating employed to avoid contamination (by choosing material from a geochemical closed system) is described. A petrographic analysis is necessary to ensure the quality of the samples. Terrace-mound, fissure-ridge, eroded sheets and range-front trave rtine deposits occur in the Alhama de Murcia fault zone. At Carraclaca a 15 m amplitude monocline fold was formed by the reverse movement of this fault which has been active since the late Pleistocene. The first available absolute ages for deformed and undeformed travertines yield a vertical slip rate of 0.08mm/yr. It is possible to estimate 4818 yr of recurrence time for the northern branch given the slip per event on alluvial deposits in the southern branch of the Alhama de Murcia fault.